From what Ive read everybody in a squad will get full BEP for every kill long as they are in the area. Now if you are running around inside a facility with a squad of a 10 AI MAXs and 4 armor repair guys you are gonna be getting MAD BEP
Running Solo all the BEP you get is what you kill rather then what your friends kill too.
But I think the higher advance rates will be happening later rather then sooner. Need more time for people to hear about PS and join. More people=more targets
So beginning= 3-3.5 months for BR20. After a year prob 1.5-2.5 months for the same player to hit BR20.